The present invention relates generally to techniques and methods to filter optical wavelengths for spectroscopy, protection from intense radiation, monochromatizing, and analyzing optical radiation, and more particularly to a solid colloidal rejection filter and a method for constructing a solid colloidal rejection filter.
Wavelength selection and wavelength selection elements are necessary in many optical measurements and techniques. Common elements are color filters and diffraction gratings. Color filters are usually broad band and of low efficiency. The best are multilayer dielectric filters with narrow band pass of about 7.5 nm but with maximum throughputs of less than 50%.
Diffraction gratings which disperse the wavelengths have the added advantage of being tunable and useful for low intensity light. However, diffraction gratings are necessarily bulky, fragile, and require multiple gratings to reject high intensity scattered light.
Colloidal optical wavelength filters have been developed that are wavelength selective by Bragg diffraction and are highly efficient with a narrow bandpass. Filters of this type have applications in spectroscopy, radiation monitoring, and laboratory techniques. These colloidal filters are suspensions of micro-spheres in liquids. U.S. Pat. No. 4,632,517 to Asher discloses such a filtering device having a crystalline colloidal structure formed by dispersing electrically charged particles, such as polystyrene spheres, within an appropriate liquid. However, these filters are short-lived and suffer from environmental limitations that are a characteristic of the liquid and the method of containment. In the field, such filters are inherently fragile. Use of liquid, as the suspending medium causes the further problem of thermal lensing with intense radiation, and the properties of the liquid change as ions leach from the containment walls of the filter. An additional problem is that the refractive index of the filter is limited by the requirements of the ionic strength of the suspending liquid.
Accordingly, an object of this invention is to provide new and improved methods and apparatus for filtering optical wavelengths for purposes of spectroscopy, protection from intense radiation, and monochromatizing.
Another object of this invention is to provide new and improved methods and apparatus for analyzing optical radiation.
Yet another object of this invention is to provide new and improved methods and apparatus for filtering optical wavelengths in which the filter has a constant refractive index.
Still another object of this invention is to provide new and improved methods and apparatus for filtering optical wavelengths that have fewer environmental limitations, possess longer lives, are less fragile and can be used in the field.
A further of object of this invention is to provide new and improved methods and apparatus for filtering optical wavelengths that maintains constant filter properties.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.